import java.util.Scanner;

/**
 * Created with Intellij IDEA.
 * Description;
 * User:墨琦
 * Data:2023-03-07
 * Time:14:01
 */
public class Text {
    public static int max2(int x)
    {
        if(x<=1)
            return 1;
        else
            return max2(x-1)+max2(x-2);
    }

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int x=sc.nextInt();
        System.out.println(max2(x));
    }
}
